1. Technical Field
The present invention relates to a technology for suppressing a stationary wave using resonance of a pipe.
2. Background Art
When a sound wave of a specific frequency is irradiated in a space which is enclosed by walls, it is known that stationary waves are generated by reciprocation of the sound wave between the wall surfaces of the space, thereby having a harmful effect on the audio property of an audio appliance. In Japanese Patents Nos. 2606447 and 3763682, and JP-A-2008-131199, technologies for suppressing the stationary wave in a speaker which is one example of the audio appliance are disclosed. The speaker apparatus disclosed in Japanese Patent No. 2606447 includes a speaker unit, a cabinet built equipped with the speaker unit, and a Helmholtz resonator installed in the cabinet. A neck length L and a cavity volume V of the speaker apparatus are designed so that the Helmholtz resonator is resonated at the same frequency as a stationary wave which is generated in the cabinet. With the speaker apparatus, in the case where the stationary wave is generated in the cabinet, the Helmholtz resonator develops a resonance phenomenon, and thus the stationary wave is attenuated by the resonance phenomenon. The speaker apparatus disclosed in Japanese Patent No. 3763682 includes a speaker unit, a cabinet equipped with the speaker unit, and an audio pipe (open pipe) having an open end and a closed end. The audio pipe of the speaker apparatus has a pipe length L of ¼ times as much as the minimum resonance mode of the stationary wave which is generated in the cabinet. The audio pipe is accommodated in the cabinet in a posture in which a position of the open end is close to a position of a loop of sound pressure (node of particle velocity) of the stationary wave in the cabinet. For the speaker apparatus, when the stationary wave (stationary wave having wavelength of four times of the pipe length L) is generated in the cabinet, a resonance wave is generated in the audio pipe. The resonance wave has a node of the sound pressure (loop of particle velocity) at the open end of the audio pipe, and a loop of the sound pressure (node of particle velocity) at the closed end. With the speaker apparatus, a deviation in distribution of the sound pressure in the cabinet is relieved, and thus the stationary wave in the cabinet is attenuated. JP-A-2008-131199 also discloses a technology similar to that disclosed in Japanese Patent No. 3763682.